There exists a long-felt need for safe, inexpensive, easy-to-use, and reliable technologies for energy storage. Large scale energy storage enables diversification of energy supply and optimization of the energy grid, including increased penetration and utilization of renewable energies. Existing renewable-energy systems (e.g., solar- and wind-based systems) enjoy increasing prominence as energy producers explore non-fossil fuel energy sources, however storage is required to ensure a high quality energy supply when sunlight is not available and when wind does not blow.
Electrochemical energy storage systems have been proposed for large-scale energy storage. To be effective, these systems must be safe, reliable, low-cost, and highly efficient at storing and producing electrical power. Flow batteries, compared to other electrochemical energy storage devices, offer an advantage for large-scale energy storage applications owing to their unique ability to decouple the functions of power density and energy density. Flow batteries are generally comprised of negative and positive active material electrolytes, which are flowed separately across either side of a membrane or separator in an electrochemical cell. The battery is charged or discharged through electrochemical reactions of the active materials inside the electrochemical cell.
Existing flow batteries have suffered from the reliance on battery chemistries and cell designs that result in either high cell resistance or active materials crossing over the membrane and mixing. This phenomenon results in low cell and system performance (e.g. round trip energy efficiency) and poor cycle life, among others. To be effective, the flow battery chemistry and cell components must be chosen and optimized to afford low cell resistance and low active material crossover. Despite significant development effort, no flow battery technology has yet achieved this combination. Accordingly, there is a need in the art for improved flow battery chemistry and cell design characteristics.